DE19539854A1 - Oil-soluble nitrogen-free corrosion inhibitors with good buffer effect - Google Patents

Abstract

Proposed is the use, as corrosion inhibitors in oil-containing liquids, of nitrogen-free aromatic hydroxy compounds with a phenolic hydroxy group and with a pKS-value for the phenolic hydroxy group in the range 7.0 to 11, represented by esters or ketones.

Description

The invention relates to novel oil-soluble corrosion inhibitors for oil-containing Liquids, for example, for oil-containing coolant emulsions and their concentrates. They are free from sewage technical reasons Nitrogen and are characterized by a good buffer effect, so that the alkaline pH of the emulsion despite a possible acid entry and / or microbiological acid development for a longer period of time can be maintained.

The protection of corrosion-prone metals such as iron, alumi aluminum, zinc, copper or their alloys from corrosion is a weitge fanned technical task. It arises in particular when the Metal parts not yet with a due to their processing state permanently corrosion-protective coating such as a paint be are covered. Examples include metal parts during technical Bear processing stages such as, for example, cutting or non-cutting shaping or cleaning. To prevent corrosion during or between each loading To prevent or contain steps in the process, you bring the Me tallow surfaces with corrosion inhibitors in contact, which is a tempo effect corrosion protection. The corrosion inhibitors can at For example, constituents of water-mixed coolant emulsions, Cleaning emulsions or anticorrosive emulsions.

Cooling lubricants are preparations / mixtures used in metal cutting tion and during metal forming for cooling and lubricating the workpieces be used. The main processing methods that are different the type of movements that make up the machined part and tool, and distinguished by the geometry of the parts to be produced  as milling, turning, drilling and grinding as cutting operations as well as rolling, deep-drawing and cold extrusion as non-cutting deformations.

The common principle of machining metalworking methods is that the tool cutting edge engages in the material while a chip lifts off the surface and creates a new surface. For the Zer Divide the material very high pressures are required. By the Ver formation of the chip and due to the friction occurring under pressure ent is heat, the workpiece, the tool and especially the chips on heated.

The desired effect of the use of cooling lubricants is therefore the Lowering the temperature otherwise in the chips z. B. up to 1000 ° C. could increase, and that in the manufactured parts influence on the measure has sustainability. Another main task of the cooling lubricants is the Tool life to improve, under the influence of high Tempe wear out quickly. By using a cooling lubricant is reduces the roughness of the surfaces, since the lubricant Ver welds of tool and workpiece surface prevents and the on adherence of particles avoids. In addition, the cooling lubricant takes over The task is to remove the chips formed. This has be especially important for mass production.

Cooling lubricants are normally used in the circulation process, d. H. in the simplest case, the use of cooling lubricants on an Ein machine, the machine has a container for the cooling lubricant.

With the new version of DIN 51385 No. 1, a clear designation of the Cooling lubricants, of which non-water-miscible, water-miscible and water-mixed cooling lubricants is mentioned. According to DIN 51385, the final state is used under the terms "water-mixed" of the finished medium (mostly as oil-in-water emulsions), below "water-miscible", however, understood the state of the concentrate.

Water-mixed coolants are manufactured by the user Mixing a concentrate, the water-miscible cutting fluid, with  Process water. As a rule, about 3 to 5% aqueous emulsions manufactured. Advantage of this type of cooling lubricant is the good cooling effect, which is based on the thermal properties of the water. By the good Cooling effect, it is possible to achieve very high operating speeds and thereby increase the productivity of machines. The lubrication The effect of the water-mixed cooling lubricants is sufficient for most applications working method in the cutting production. Another before in part, the low costs associated with the possible mix of the Kon be achieved with water. Disadvantage of water-mixed cooling lubricants is that they emp against infestation by microorganisms emp are more sensitive and therefore require more control and care. The estate The presence of water can cause rusting and can damage sensitive metals attack. Water-based cooling lubricants are used today for almost all Chipping types used. In addition to the demand for rust protection for the Machinery and machined iron alloy parts are required that non-ferrous metals are not attacked.

The table shows a summary of the requirements for what mixable and water-mixed cooling lubricants:

• - Cooling and lubricating effect
• - rust protection
• - no attack on non-ferrous metals
• - Toxicological safety especially skin compatibility
• - no foaming
• - no attack on paints and seals
• - Emulsion stability
• - no gluing or resinification
• - good miscibility
• - pleasant smell
• - clean appearance
• - good filterability
• - easy disposal.

The requirements for the rust protection effect of cooling lubricants are especially high, since after machining with cooling lubricants in the  Generally no drying is possible. The parts usually get wet placed in boxes and should not rust even when wet. to Testing of the rust protection effect are used in the development and also in the Control of in-use solutions is often the test used with cast chips according to DIN 51360/2.

The rust protection effect of the cooling lubricants is influenced by a Set of factors. So did the quality of the mixture used for the mix Water a big influence. The water hardness, but above all Chlorides and sulfates, worsen the antirust effect of the solution. To make matters worse with longer use of coolants that the concentration of salts constantly increases, since parts of the emulsion ver steam and the losses are replenished with saline water.

Non - water - miscible and water - miscible cooling lubricants, as far as they are Application state Emulsions are often based on mineral oil. The mineral oil qualities used are predominantly combinations of paraffinic, naphthenic and aromatic hydrocarbon compound fertilize. In addition to mineral oils also have so-called synthetic lubricants ("synthetic oils") such as polyolefins, polyalkylene glycols and glycol ethers, natural ester oils as well as synthetic esters and their derivatives meaning.

In order to meet the requirements of the practice, the water-miscible cooling lubricants in addition to the base oil various compo contain nents. The most important substance groups are the emulsifiers, Corrosion protection additives, biocides, EP additives, polar additives, anti-fog additives, anti-aging agents, solid lubricating additives and defoamers.

Emulsifiers (eg surfactants, petroleum sulfonates, alkali soaps, Al kanolaminseifen) stabilize the fine distribution of oil droplets in the aqueous working fluid, which is an oil-in-water emulsion. The Emulsifiers provide by volume an important group of additives the water-miscible cooling lubricants.

Usual corrosion protection additives (eg alkanolamines and their salts, Sulfonates, organic boron compounds, fatty acid amides,  Aminodicarboxylic acids, phosphoric esters, thiophosphonic esters, Dialkyldithiophosphates, mono- and dialkylarylsulfonates, benzotriazoles, Polyisobutenbernsteinsäurederivate) are the rusting of Metalloberflä prevent it. In the past, nitrite was often used as a corrosion inhibitor However, because of its toxicity and environmental especially because of the risk of formation of carcinogenic nitrosamines ver is pounding. Some anti-corrosive additives have emulsifying properties at the same time Properties and therefore find their application as an emulsifier. Biocides (eg phenol derivatives, formaldehyde derivatives, Kathon MW) prevent the growth of bacteria and fungi. EP additives (eg ge sulfurized fats and oils, phosphorus compounds, organochlorine Compounds) are micro-welds between metal surfaces at prevent high pressures and temperatures. Polar accessories (eg natural fats and oils, synthetic esters) increase the smelting insurance properties. Aging inhibitors (eg organic sulfides, Zinc dithiophosphates, aromatic amines) ensure a long Ge service life of the cooling lubricants.

A central position among the additives take the alkanolamines and Alkanolamine derivatives, which are present in a large number of water-miscible Cooling lubricants are used as corrosion protection additives. also they guarantee in conjunction with carboxylic acids by their good Pufferka capacity a certain pH constancy of aqueous working emulsions. The pH constant comes with regard to the emulsion stability and the Anti-rust protection is of particular importance. Reaction products of Alkanolamines with boric acid have a growth-inhibiting effect on bacteria and Molds and therefore improve the service life of cooling lubricant materials.

A disadvantage of the alkanolamines and alkanolamine derivatives is that they during the practical use with nitrosating substances, eg. B. bacterial ge Formed nitrite or nitrogen oxides in the air, can react and thereby be converted into nitrosamines. For example, can be in water-mixed cooling lubricants containing ethanolamines, nitrosodiethanolamine (NDELA) be formed.  

Nitrosamines can cause cancer on various organs after animal experiments (eg. Stomach, lungs, bladder, liver, esophagus). That's why some are Nitrosamines, e.g. As well as NDELA, in the German Hazardous Substances Ordinance as carcinogenic classified. To avoid health hazards for the operators of metalworking machines, therefore, the formation be avoided by nitrosamines.

There is therefore a need for corrosion inhibitors that are toxicologically un are more questionable and for environmental reasons as possible no stick substance or phosphorus. This can be done, for example Carboxylic acids on. When using carboxylic acids or their salts is however, their limited oil solubility is often detrimental. This he hampers the formulation of oily active substance concentrates from which Mix with water to form ready-to-use emulsions. The carboxylic acids usually do not show sufficient Pufferkapa in the alkaline pH range of the ready-to-use emulsion usually between about 8 and about 9.5. A run out However, buffering capacity would be technically advantageous because alkaline pH values for the corrosion protection effect are advantageous. By acid entry and microbiological processes, the pH during the However, use decrease, so that the corrosion protection effect lost goes. By a high buffering capacity of the emulsion, this pH reduction prevented or delayed.

The use of carboxylic acids as corrosion inhibitors in at For example, coolants, cleaners and corrosion protection emulsions is common in the art. For example, the DE A-42 29 848 a coolant emulsion, its corrosion protection system on a combination of long-chain fatty acids, short-chain fatty acids, Dimer fatty acids and aromatic carboxylic acids such as Ben zoesäure or salicylic acid is based. Here are the carboxylic acids with Neutralized potassium hydroxide. This system does not contain a buffer component in the sense of the present invention.

German patent application DE-A 43 23 909 teaches two-component agents for cleaning and / or passivation of metal surfaces, wherein a  Component containing corrosion protection agents. These are the Korro anion inhibitor drugs selected from

• i) at least one carboxylic acid of the general formula (III): R-COOY (III) where R is a straight-chain or branched, saturated or unsaturated alkyl or alkenyl radical having 5 to 21 C atoms or a radical of the general formula (IV) R¹ = saturated, straight-chain or branched alkyl radical having 6 to 18 C atoms and Y is hydrogen, an alkali metal ion equivalent or an ammonium ion,
• ii) substituted benzoic acids,
• ii) benzenesulfonamidocarboxylic acids,
• iii) aliphatic dicarboxylic acids having 2 to 36 carbon atoms, and
• iiii) the salts of the acids mentioned under i) to iii) and their mixtures cal.

Also, this system does not include buffer components for stabilization the alkaline pH at acid entry or acidification.

In the German patent application DE-A 44 44 878 water-soluble stick-free corrosion inhibitors are described with good buffer effect, the keynote of a mixture of carboxylic acid anions containing 6 to 44 carbon atoms and aro hydroxy compounds with a pK _s value for the hydroxy group in the range from 7.0 to 11 exist. These corrosion inhibitors are suitable for aqueous systems. However, because of their limited oil solubility, they are not suitable for the preparation of oily concentrates for cooling lubricant, cleaning or corrosion protection emulsions.

The invention is based on the object, nitrogen-free oil-soluble Kor rosin inhibitors used in oil solutions and in ready-to-use oil-in-water emulsions for improved buffering effect and thus lead to prolonged corrosion protection.

This object is achieved by using nitrogen-free aromatic hydroxy compounds having phenolic hydroxy group, which have a pK _s value for the phenolic hydroxy group in the range of 7.0 to 11 and are esters or ketones, as corrosion inhibitors for oily liquids.

The aromatic hydroxy compounds are preferably selected from mono-, di- or tricyclic aromatic hydroxy compounds of general formula (I)

HO - Aroma - Y (I)

where "Arom" represents a mono-, di- or trinuclear aromatic six-membered carbocyclic aromatic six-membered ring system of the type of benzene, naphthalene, anthracene or phenanthrene, the further substituents Y, OH and / or alkyl, hydroxyalkyl and / or hydroxyalkyl ether radicals having 1 to 4 C atoms can carry, and
Y represents a group - (CH₂) _n - X in which
n is an integer in the range 0 to 4 and
X is selected from substituents C (O) R, COOR, PO₃HR, PO₃R₂ and SO₃R, wherein
R is a methyl, ethyl or a linear or branched, saturated or unsaturated alkyl radical having 3 to 22 carbon atoms or an alkylaryl radical having 7 to 30 carbon atoms. Particularly preferred are compounds in which the group X is bonded directly to the aromatic ring. Then in the group Y the index n = 0.

Preferably, the aromatic hydroxy compounds are mononuclear and ent speak the general formula (II)

wherein Y has the meaning given in claim 2 and R¹, R², R³ and R⁴ independently of one another a group Y, H, OH or an alkyl, Hydroxyalkyl or hydroxyalkyl having 1 to 4 carbon atoms. Again, the group X is preferably directly with the aromatic Ring, so that in the definition of Y n = 0 means. virtue The aromatic hydroxy compounds are selected from the group consisting of verbin compounds of general formula (II) containing only one substituent Y ent th and in which the substituents R¹, R², R³ and R⁴ are hydrogen.

The aromatic hydroxy compounds may be, for example Esters of aromatic carboxylic, sulfonic and / or phosphonic acids. Here, the esters are preferably selected from alkyl esters of m- or p-hydroxybenzoic acid having one, two or three carbon atoms in the Alkyl group. Especially suitable examples are the ethyl esters or n-Propyl ester of p-hydroxybenzoic acid The corresponding esters of 4-phenolsulfonic acid can also be used.

The aromatic hydroxy compounds may also be ketones act, d. H. the substituent X in the general formulas I and II can represent a group C (O) R. Preferably, this is directly to the aroma Tied ring. In this case, those ketones are preferred in which R an alkyl group having 1 to 4 carbon atoms. On According to the invention suitable example is 4-hydroxyacetophenone.

The corrosion inhibitors are used in liquids, the pure ones Represent oil or oil solutions, such as engine, engine or Compressor oils, hydraulic oils, corrosion protection oils, rolling oils or not  water-miscible cooling lubricants. In the application form, the oil containing liquids but also aqueous emulsions with an oil content between about 0.3 and about 90% by weight. Examples of such Emulsions are water-miscible or water-mixed with coolants an oil content of between about 10 and about 90% by weight in the water-miscible Concentrate or between about 0.3 and about 5 wt .-% in the water-mixed coolant emulsion. Further fields of application are Cleaning or anti-corrosive emulsions with similar oil contents.

While aqueous emulsions can cause immediate corrosion on contact with metal surfaces, purely oily systems are initially corrosion-inhibiting due to their freedom from water. However, since in the latter case, currency is often used to introduce water from the environment, pure oily systems are initially corrosive to metal surfaces over time. In both cases, therefore, corrosion inhibitors are required. The corrosion inhibitors to be used according to the invention are particularly effective when the water phase has a pH in the range from about 7 to about 11. These are, for example, customary pH values for coolant lubricant or anticorrosion emulsions, the pH values preferably being between about 8 and about 9.5. The invention is based on the finding that oil-soluble aromatic hydroxy compounds display a particularly good buffering effect in this pH range, if the _pK a is for the hydroxy group in the range of about 7 to about 11, and more preferably between about 8 and about 9.5 ,

The _pK a value is known to be the negative decadic logarithm of the acid constants K _S which is generally known as a thermodynamic quantity and represents a measure of the completeness of the proton transfer reaction of the acid to water and thus the acid strength. Details can be found in textbooks of general chemistry. HRChristen was mentioned by way of example: "Fundamentals of General and Anorganic Chemistry", Verlag Sauerländer, Aarau and Disterweg.Salle, Frankfurter, 4th edition 1973, pp. 353-372. The _pK a value for the hydroxy group of the aromatic hydroxy compounds according to the invention refers to the acid-base reaction of the hydroxy group of the aromatic hydroxy compound with water.

Present invention, since such hydroxyl compounds are used whose _pK a is for the hydroxy group of the aromatic hydroxy acids in the range of 7.0 to 11, is to be expected that the hydroxy groups are deprotonated in the selected pH range in part. To the possibility of determination of the _pK a values of the weakly acidic hydroxy groups is put to the literature referred Konopik: N. Konopik, O. Leberl "Dissoziationskon constants of very weak acids," Monatshefte 80 (1949), pp 660-662 , Further pK _S provisions are contained in: B. Jones, JC Speakman: "Thermodynamic Dissociation Constants of Hydroxy and Alkoxybenzoic Acids", J. Chem. Soc. 1944, pp. 19-20. Accordingly have m- and p-hydroxybenzoic acid _pK a values of 9.94 or 9.39 in. The _pK a value of 4-phenolsulfonic acid for the phenolic hydroxy group was determined to be 8.9.

The aromatic hydroxy compounds are used in an amount based on the oil content of the oily liquid, used from 0.1 to 30 wt .-%, wherein amounts of 0.5 to 20 wt .-% are preferred. For this ingredient held the oily liquids in the ready-to-use Formulation buffer capacities greater than 1 on. Here is the Buffer capacity defined as the consumption of 0.1 normal hydrochloric acid, measured in ml to the pH of 50 g of the preparation of a pH from 9.3 to a pH of 8.

For the long-term stability of the appli- It is preferable for this ready-to-use preparation to have a buffering capacity ranging from 1 to 8.

In the context of the invention are also corrosion-inhibiting oily Liquids containing one or more of the invention used aromatic hydroxy compounds in an amount based on the oil content the oily liquid, from 0.1 to 30 wt .-%, preferably from 0.5 to 20 wt .-%, contained. In doing so, these corrosion-inhibiting oil containing liquids as such, for example as engine, engine or compressor oil, hydraulic oil, anticorrosive oil, rolling oil or as non-water-miscible cooling lubricant present. Among the Er It may be due to falling corrosion-inhibiting oily liquids but also to oil-in-water emulsions with an oil content between  about 0.3 and about 5 wt .-% act. Examples of such emulsions are water-mixed cooling lubricants, corrosion protection and cleaning emuls sions.

embodiments Concentrate A (comparison)

It became a concentrate of a water-miscible coolant emulsion prepared by adding the following components in the order given mixed together:

component parts by weight completely desalinated water 2.9 1,2-propanediol 7.7 tall oil fatty acid 5.9 Mineral oil (white oil pioneer 4556, Hansen & Rosenthal) 35.7 Potassium hydroxide flakes 7.0 Dimer fatty acid (Empol 1022, Emery) 11.7 60% acetic acid 0.8 Oleyl / cetyl fatty alcohol × 2 ethylene oxide 16.1 caprylic 7.1 tallow 1.9 Preservatives (Bacillat 1110, Bode Chemie) 3.2

Concentrate 1 (according to the invention)

95 parts by weight of concentrate A were mixed with 5 parts by weight of p Hydroxybenzoic acid ethyl ester (commercially available).

Concentrate 2 (according to the invention)

95 parts by weight of concentrate A were mixed with 5 parts by weight of p-hydroxybenzoic acid n-propyl ester (commercially available).

Concentrate 3 (according to the invention)

95 parts by weight of concentrate A were mixed with 5 parts by weight of 4-hydroxyacetophenone (commercially available).  

To test the corrosion protection effect were from the above ge Concentrates called ready to use cooling lubricant emulsions Herge by adding 3 parts by weight of concentrate with 97 parts by weight of water ver sat. The corrosion protection effect of these emulsions was according to DIN 51360/2 tested by applying chips of gray cast iron on filter paper with the emulsion were wetted. After 2 hours, the corrosion marks were on the Filter paper according to the specified in said DIN document Comparative scale rated. In this case, a degree of corrosion 0 means no Kor rosion, and corrosion degree 4 very strong corrosion. The degree of corrosion 1 to 3 are in between. The following degrees of corrosion were observed: Emulsion of concentrate A: degree of corrosion 2, emulsion of concentrate 1: Degree of corrosion 1 to 2, emulsion of concentrate 2: degree of corrosion 1, Emulsion of concentrate 3: degree of corrosion 1.

The buffer capacity was tested on emulsions prepared by adding 2 Parts by weight of the concentrates with 98 parts by weight of water were obtained. The consumption of 0.1 normal hydrochloric acid in ml was determined to be 50 g of the emulsions from an initial pH of 9.3 to a pH to titrate from 8. If the pH before the titration was below 9.3, it was adjusted by the addition of sodium hydroxide solution to this value. resulting nis: emulsion of concentrate A: buffer capacity 0.45 ml, emulsion off Concentrate 1: buffering capacity 1.54 ml, emulsion of concentrate 2: buffer capacity 1.10 ml, emulsion of concentrate 3: buffer capacity 2.0 ml.

Claims (17)

1. The use of nitrogen-free aromatic hydroxy compounds having phenolic hydroxy group, which have a pK _s value for the phenolic hydroxy group in the range of 7.0 to 11 and esters or ketones, as corrosion inhibitors for oily liquids liq. 2. Use according to claim 1, characterized in that the aromatic hydroxy compounds are selected from compounds of the general formula (I) HO - Arom - Y (I) wherein "aroma" is a mono-, di- or trinuclear aromatic carbocyclic six-membered aromatic system is of the benzene, naphthalene, anthracene or phenanthrene type, which may carry further substituents Y, OH and / or alkyl, hydroxyalkyl and / or hydroxyalkyl ether radicals having 1 to 4 carbon atoms, and
Y represents a group - (CH₂) _n - X in which
n is an integer in the range 0 to 4 and
X is selected from substituents C (O) R, COOR, PO₃HR, PO₃R₂ and SO₃R, wherein
R is a methyl, ethyl or a linear or branched, saturated or unsaturated saturated alkyl radical having 3 to 22 carbon atoms or egg nen alkylaryl having 7 to 30 carbon atoms. 3. Use according to claim 2, characterized in that in the general my formula (I) in the definition of the group Y n = 0.   4. Use according to one or both of claims 1 and 2, characterized in that the aromatic hydroxy compounds are selected from compounds of the general formula (II) wherein Y has the meaning given in claim 2 and R¹, R², R³ and R⁴ independently of one another mean a group Y, H, OH or an alkyl, hydroxyalkyl or hydroxyalkyl ether radical having 1 to 4 C-atoms. 5. Use according to claim 4, characterized in that in the defi nition of Y n = 0 means. 6. Use according to one or both of claims 4 and 5, characterized ge indicates that the aromatic hydroxy compounds are selected from compounds of the general formula (II) which have only one Substituents Y and in which the substituents R¹, R², R³ and R⁴ is hydrogen. 7. Use according to one or more of claims 1 to 6, characterized characterized in that it is the aromatic hydroxy compounds esters of aromatic carboxylic, sulfonic and / or phosphonic acids han delt. 8. Use according to claim 7, characterized in that the esters are selected from alkyl esters of m- or p-hydroxybenzoic acid with one, two or three C atoms in the alkyl group. 9. Use according to one or more of claims 1 to 6, characterized characterized in that it is the aromatic hydroxy compounds is about ketones.   10. Use according to claim 6, characterized in that the group Y in the general formula 2 represents a substituent C (O) R, wherein R represents an alkyl group having 1 to 4 carbon atoms. 11. Use according to one or more of claims 1 to 10, characterized characterized in that the aromatic hydroxy compounds in a Amount, based on the oil content of the oily liquid, of 0.1 be used to 30 wt .-%. 12. Use according to claim 11, characterized in that the aroma tables hydroxy compounds in an amount based on the oil content the oily liquid, from 0.5 to 20 wt .-% are used. 13. Use according to one or more of claims 1 to 12, characterized characterized in that the oil-containing liquid is a Ma engine, engine or compressor oil, a hydraulic oil, a corrosive oil, a rolling oil or a water-immiscible cooling lubricant acts. 14. Use according to one or more of claims 1 to 12, characterized characterized in that the oil-containing liquid is a aqueous emulsion with an oil content between 0.3 and 90 wt .-% han delt. 15. Use according to claim 14, characterized in that it is at the aqueous emulsion to a water-miscible or water-mixed Cooling lubricant with an oil content between 10 and 90 wt .-% im water-miscible concentrate or between 0.3 and 5 wt .-% in the mixed with water coolant emulsion. 16. Corrosion-inhibiting oily liquid containing one or more Aromatic hydroxy compounds according to one or more of the claims 1 to 10 in an amount based on the oil content of the oil-containing Liquid, from 0.1 to 30 wt .-%.   17. corrosion-inhibiting oily liquid according to claim 16, characterized characterized in that it is an oil-in-water emulsion with an oil content between 0.3 and 5 wt .-% is present.